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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/110724] Unnecessary alignment on branch to
 unconditional branch targets
Date: Tue, 18 Jul 2023 17:48:28 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110724

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2023-07-18
     Ever confirmed|0                           |1

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The generic tuning is:
  "16:11:8",                            /* Loop alignment.  */
  "16:11:8",                            /* Jump alignment.  */
  "0:0:8",                              /* Label alignment.  */

The the operands are described as:
https://gcc.gnu.org/onlinedocs/gcc-13.1.0/gcc/Optimize-Options.html#index-f=
align-functions
```
-falign-functions=3Dn:m:n2
...
Examples: -falign-functions=3D32 aligns functions to the next 32-byte bound=
ary,
-falign-functions=3D24 aligns to the next 32-byte boundary only if this can=
 be
done by skipping 23 bytes or less, -falign-functions=3D32:7 aligns to the n=
ext
32-byte boundary only if this can be done by skipping 6 bytes or less.

The second pair of n2:m2 values allows you to specify a secondary alignment:
-falign-functions=3D64:7:32:3 aligns to the next 64-byte boundary if this c=
an be
done by skipping 6 bytes or less, otherwise aligns to the next 32-byte boun=
dary
if this can be done by skipping 2 bytes or less. If m2 is not specified, it
defaults to n2.
```

So align jumps to 16 byte if 11 or less bytes can be used or 8 byte alignme=
nt
Which is exactly what this does:
        .p2align 4,,7          # <-- unnecessary alignment
        .p2align 3=